Australian surveys on incidence and control of blowfly strike in sheep between 2003 and 2019 reveal increased use of breeding for resistance, treatment with preventative chemicals and pain relief around mulesing.

Abstract

Blowfly strike or cutaneous myiasis, caused principally by the Australian sheep blowfly Lucilia cuprina is endemic to Australian sheep producing areas and is a major cause of suffering and economic loss. This article reports incidence and control practices as determined by three cross-sectional surveys of Australian sheep farmers covering the years 2003 (n=1365), 2011 (n=575) and 2018 (n=354) with more questions relating to blowfly strike in the latter two surveys. Breech strike was reported at a higher rate than body strike in all survey years. Reported annual incidence of breech strike ranged from 2.2 to 4.7% of sheep nationally with minor differences between ewes and lambs. The incidence of body strike ranged from 1.0 to 7.1% with higher incidence in younger sheep in all years. The use of fixed time routine preventative chemical treatments increased during the survey period (43%, 46% and 66%, in 2003, 2011 and 2018 respectively) with dicyclanil (54%-58%) and cyromazine (23-36%) the main insecticides used for control since 2011. The use of the Mules operation (mulesing) to remove skin wrinkles from the breech area as a preventative modification did not change between 2011 and 2018 (47% in both), however, the use of pain relief at mulesing of replacement ewe lambs increased substantially between 2011 (59%) and 2018 (87%). The most commonly used methods to assist with flystrike control were timing of crutching (clipping of wool from susceptible areas) and shearing, with few respondents destroying maggots from treated sheep (21-26%) and very low use of fly traps (5-8%). Phenotypic selection of ewes for reduced susceptibility to flystrike based on visual traits was practiced by 61% of respondents in 2011 and 56% in 2018. Selection of rams for reduced susceptibility using estimated breeding values increased from 10% in 2011 to 17% in 2018. Breeding for resistance was the most commonly nominated (21%) most important change made to flystrike management in 2018. The results indicate that concern for sheep welfare has increased with almost universal use of pain relief at mulesing. Increased use of selection for blowfly resistance indicates farmer commitment to planning for a future without mulesing, although the practice remains prevalent. An increase in the reliance on preventative chemical treatments increases the risk of insecticide resistance.